Metabolic and innate immune responses, two primitive systems critical for the long-term homeostasis of multi-cellular organisms, have evolved to promote cooperative, adaptive responses against diverse environmental challenges. Conversely, over-nutrition associated with modern high-calorie diets often leads to mis-regulation of metabolic-innate immune interactions and the development of metabolic diseases, such as obesity and type II diabetes. Thus, there is a critical need to characterize the mechanistic connection and coordination of these responses. The goal of our research is to use the fruit fly, Drosophila melanogaster, as a simple model system to uncover the origin of metabolic-innate immune interactions in order to advance our knowledge of diet-mediated metabolic imbalances in humans. In this proposal, we plan to characterize a novel interaction between the innate immune transcription factor NFkB and the insulin-responsive metabolic transcription factor Foxo. NFkB transcription factors, evolutionarily conserved regulators of innate immunity, are emerging as a critical node in the bidirectional communication and coordination of metabolic and innate immune signaling pathway interactions. Using Drosophila, an important model organism for the study of metabolism and integrative physiology, we have previously established a role for Foxo transcriptional function in the control of NFkB-mediated innate immune responses. We now provide further evidence that diet-dependent NFkB activity in the Drosophila fatbody (similar to mammalian adipose tissue) can also impact lipid homeostasis through the regulation of Foxo function; establishing a cellular Foxo/NFkB 'homeostatic module' that governs metabolic and innate immune responses through mutual regulation of transcription factor activity. Drosophila provide an invaluable, genetically tractabl model to characterize this module, as these signaling networks are conserved from flies to humans. Interestingly, the Drosophila fatbody combines functions of nutrient and pathogen sensing organs, highlighting the inherent association between metabolic state and innate immune function. There are three specific aims to this proposal: (i) To assess the role of fatbody-specific NFkB activity in the regulation of lipid homeostasis; (ii) to characterize the molecular and cellular interaction between Foxo and NFkB; and (iii) to assess the role of fatbody-specific Foxo/NFkB interactions in the regulation of nutrient- dependent metabolic adaptation. Using the powerful genetic tools available in Drosophila, coupled with integrative molecular, cellular, physiological, and high-throughput diet-mediated approaches, we will define this interaction at multiple levels of biological organization. Exploiting Drosophila to explore th origin of metabolic-innate immune interactions holds tremendous promise for an enhanced rate of uncovering both novel disease mechanisms and pharmaceutical targets aimed at treating the underlying metabolic imbalances that lead to pathologies such as obesity and type II diabetes.